Obtaining Transmit Parameter in Initial Scanning for Channel

Once a DL-MAP message has been detected, the MAC sublayer will listen for downlink and uplink transmission parameter. By listening for UCD messages from the Base Station (BS), the Subscriber Station (SS) is able to determine a usable uplink channel.

UCD messages are broadcast messages, send out periodically, providing pertinent parameters for all available uplink channel, and will attempt to establish communications on suitable channel.

If communications fail on one channel, the SS will move on to next suitable channel until a connection is establish or the list has been exhausted, in which case it will begin the scanning process again.

WiMAX Network Entry and Initialization, part 1.

Once a SS senses a BS, for a network entry, it will first scans for downlink channel (DL) and trying synchronizes itself with the BS. After that, SS shall obtain transmit parameters, which are integrated in the Uplink Channel Descriptor (UCD), Uplink (UL)-MAP, and Downlink (DL)-MAP. The final step would be to complete initial ranging.

The BS is required to discover different received ranging codes, approximate the timing offset and the power for every user that bears and initial ranging code. The BS then broadcast the detected ranging codes with some change instruction for the proper timing and power level. Other than that, the status notifications of either ranging successful or retransmission are also broadcasted.